Paper or plastic? Credit or cash? Sweet or unsweet? Oh, the questions of the ancients have perplexed us so. Yet we continue to argue points for each side with equal validity and fervor. An argument closer to our hearts that seems to come up regularly is whether a carburetor or electronic fuel injection is the superior form of fuel delivery in a high-performance engine.

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The debate usually goes something like this: "Carburetors cool the engine and injectors let hot air in."

"Yeah, well injectors are more precise and can shoot the gas right into the combustion chamber."

"Yeah, well carburetors are cheaper."

"Yeah, well injectors can run even if the car is vertical or upside down!"

"Yeah, well where is the oil in your engine if the car is upside down?"

"Yeah, well my dad can beat up your dad."

And so it goes.

Since the beginning of internal combustion time, basic carburetors have been taking advantage of the Bernoulli effect as their primary method of delivering atomized fuel to the awaiting engine. Though visually quite different from what we see today, the design first patented by Karl Benz in 1896 showed the basic simplicity by which a carburetor could properly meter fuel based on the load and rpm of the engine. In a nutshell, low pressure in the manifold (open throttle) would invite a rush of air through the carburetor. As the high-velocity air passed through, it would draw fuel through carefully placed holes in the carb bore and send it down into the combustion chamber. Tuning is done primarily via fuel jets and air bleeds that are swapped out to richen or lean out the engine, and acceleration enrichment is accomplished usually through the use of an accelerator pump and adjustable or replaceable actuators like accelerator pump cams. There are entire books on the theory and function of carburetors that we won't go into on the next few pages, but in essence, the carb is a fairly basic device that can be tuned fairly well by anyone with a little bit of patience and a good carb book.

3/20Patrick at Pro-Systems set up the Holley 950 HP carb for MME. Mark McKeown then modified the throttle shaft to attach it to a TPS sensor.

Crude forms of fuel injection have also been used as far back as the late 1800s, mostly in diesel engines, and later adapted for use in airplane engines in World War II. Planes with simple carburetors would simply empty the bowls and starve for fuel in a negative g or inverted flight situation where the injected planes had no trouble with those maneuvers. It wasn't until 1954 that Mercedes-Benz brought commercial gasoline mechanical fuel injection into the public domain. Though Robert Bosch is usually credited with being the father of electronic fuel injection, EFI, it was actually Bendix that released the first EFI system, the Electrojector, on a '57 AMC Rambler Rebel. Yes, an AMC. Bosch later snapped up the rights to the Bendix design and modified it for the famous D-, K- and later L-Jetronic systems. EFI systems typically use sensors to measure coolant temp, air temp, manifold air pressure (MAP), and throttle position at a minimum and compare these against fuel maps created by the tuner to get the engine running at peak efficiency. As with carburetors, EFI systems can be tuned fairly well by anyone with a little bit of patience, a good tuning book, and a laptop. In both cases, an oxygen sensor, a good long stretch of road, and/or a dyno make the task much easier.

4/20Sixty-pound injectors set at 42 psi were overkill, but dialing them back was not an issue with the C-Com software.

Both fuel delivery systems have had many face-lifts over the years, but the question remains: Which is better? While building an engine for the 2009 Engine Masters Challenge, Mark and Heather McKeown of McKeown Motorsport Engineering decided to tackle that question once and for all.

The McKeowns have been a dedicated racing family for many years, most notably in the NMRA and NMCA ranks, but even as far as building NHRA Pro Stock truck engines before the class was relegated to the Sportsman level. Mark was unsure whether a tried-and-true Holley 4150 was the right choice for his engine, or if the high-tech FAST XFI fuel-injection system would make the most average horsepower through a broad rpm range. With a tremendous amount of dyno tuning experience in carb and EFI situations, the quality of the tuner would be a given, and the information would be reliable.

5/20One of the reasons Mark chose the Ford Mod motor for this project was that he thought with its impressive size and SOHC moniker, it would make a great powerplant for those building kit cars like the Cobra.

The engine that MME used as their testbed was one of the millions of two-valve 4.6L Ford engines that was produced for Mustangs, Town Cars, trucks, and cop cars from 1991 through the present day. The exact specimen began its life powering a van through 200,000-plus miles of reliable service, and was thoroughly seasoned. Ford cast their blocks at two different plants and designated the skeletons as either a Romeo or Windsor casting. Different main bearings, timing gears, crank flange bolt pattern, valve covers, and cam cap designs individualize the engines, but both are equally capable in terms of durability in the 500-600hp range where most high-performance 4.6-liters draw the line from badass street/strip car to serious race engine. The McKeowns' block was bored, torque-plate honed, and fitted to a set of matching Probe H-beam rods and forged pistons via Clevite rod and main bearings.

Taking advantage of Ford's R&D efforts, Mark used the factory crank blessed with undercut and rolled fillets that are proven to reduce stress risers and increase overall strength. Many high-performance 4.6L builds use a Cobra oil pump with its steel gears and high-volume design, but with the factory standard-volume pump producing over 80 psi of pressure throughout the dyno pulls, Mark felt justified not upgrading his pump. He does stress, however, that good oil pressure is critical on 4.6L builds to let the hydraulic cam followers (i.e. lifters) work correctly.

Trick Flow's new Twisted Wedge cylinder heads were chosen for their improved design. The new castings relocate the inlet valve and runner to the "correct" side of the cam where the air and fuel don't have to make a 90-plus degree turn to enter the combustion chamber. The heads are designed for a 1.84-inch valve but replacement of the intake seats allowed Mark to install custom Manley 1.900-inch valves for better flow. COMP Cams supplied the custom hydraulic roller cams that would work with the heads. While most cam grinders list their cams' dimensions at the cam lobe itself, MME points out that due to rocker ratio and lobe design it is critical to actually measure and degree the cam specs at the valve to determine what the engine actually sees. Mark says this is especially important for overhead cam engines that aren't ground to typical pushrod engine shapes. "Cams for that thing are sort of weird anyhow. Cam durations for it being an overhead-valve motor are pretty much out the window compared to a pushrod motor." Regarding the unusual choice of running more intake than exhaust duration, he says: "I thought it was going to be pretty much intake-starved. There's just not a lot of manifold available for that thing either. I had pretty much one shot at it, and I think it could probably handle more camshaft." Noting how different the cam requirements were for OHC versus OHV engines, Mark says: "One thing I learned doing 2300s for dirt track cars years ago was that the guys around here who were building circle track 2300s were building cam specs identical to what they would if they were building a small-block Chevy or a 351 Windsor. None of these guys ever actually degreed cams on four-cylinder engines." Noting that cam card dimensions are typically measured at the cam and not the valve, a pushrod engine measures cam duration at the cam lobe and lift at the valve, whereas an OHC engine measures both duration and lift at the valve. Comparing cam cards for the two engines is like comparing apples and octopi. COMP ground as aggressive a cam as they thought they could, and even so, the factory lifters and followers were used. Racers who have messed with old OHC 2300 Ford engines know how critical it is to get valvetrain geometry right on OHC/rocker arm engines, or it will spit the rockers clean out. Mark says that using a hydraulic lifter to set up the geometry was tricky since it wanted to depress, but in the end, it worked without incident.

9/20Ingenuity popped its head up as Mark came up with his own front-mount, beltdriven distributor. Using pieces from various MSD setups, he claimed victory that the engine actually fired up and ran.

Choosing an intake manifold for such a test might seem daunting when dealing with a small-block Chevy due to the overwhelming number of options, but for the 4.6-liter the choices are few. The Edelbrock Victor Jr. intake will accommodate both a square-bore carb, and has cast-in bungs for injectors. This made the choice obvious. Only minor porting was done to the intake to make sure there were no obstructions and the runner dimensions matched the heads.

10/20Modern tuning with the laptop can be much quicker and simpler than changing jets, spilling gas over the intake, and guessing what results will come. Also, running in closed-loop mode, the computer can self-tune to a given air/fuel ratio. Advantage XFI.

For the carb setup, MME used a Pro-Systems modified Holley 950 HP. During testing, they wanted to check all the variables so they made sure to record inlet temp as well as fuel consumption, oil pressure, and water temp. Using these measurements, they could get a better view of the efficiency of the combination.

Ignition on a 4.6L engine, like an LS or late-model Hemi, is designed for a coil-on-plug, or coil-near-plug system, but Mark took a different route. Designing his own beltdriven distributor, he used MSD components such as the cap and rotor and HVC ignition coil to send fire through the spark plugs. An MSD Flying Magnet crank trigger sent a signal to the XFI computer where Mark generated the most efficient ignition table. The signal was then sent over to an MSD Digital 7 ignition box where the fire was finally released to the coil. This setup was used for both the carbureted and fuel-injected setups as it provided complete accuracy and repeatability. Another benefit to this design is that with a simple swap to a 36-1 or 60-2 crank trigger wheel (or a cam position sensor) XFI allows for individual cylinder timing and fuel changes to be made for ultra fine-tuning. With fuel injectors plugging the open holes in the intake but not obstructing flow, they ran the engine through its paces making a number of dyno pulls at various rpm levels with Shell 91 octane pump gas.

11/20Though the lobes look huge, they actually have a fairly small base circle for the design. Any alteration to the base circle forces the engine builder to change the valve tip length in order to maintain proper geometry. The roller followers float on the valve and lifter tips, and if geometry is wrong, the cam will spit them out.

Since they wanted to use this engine for the Engine Masters Challenge, they chose the 3,000-7,000 rpm range as their final comparator. Over such a broad range, typically people have claimed that a carb might make slightly better peak power but the EFI setup would trump it for overall average torque. Would that be the case here? Time would shortly tell.

12/20Edelbrock's Victor Jr. for the 4.6-liter was virtually unmodified for the engine. Though its design, by necessity, has some sharp bends in order to have any hood clearance, it clearly did not make the carbureted test suffer as expected.

The cooling effect of the carburetor was validated as the McKeowns measured a 25-degree drop in temperature from the ambient air in the dyno room to the inlet tract. A drop in temperature like that should show up as an increase in power, as the air/fuel charge would end up denser than the outside air. More oxygen equals more fuel that can be burned, which equals more power. Fuel usage was quite efficient as the carefully tuned engine was dialed in to a 13.5:1 air/fuel ratio. With those numbers and a good baseline torque/horsepower curve in the bank, Mark swapped the fuel line to a high-pressure feed, and hooked up the FAST XFI.

Like many EFI units, the FAST system controls fuel and spark over the operating range of the engine, but those are just the basics. XFI will allow the user to run up to four pre-programmed Qwik-Tunes that can be swapped out at the flick of a switch, control four stages of nitrous, and has easy Windows-based tuning with their C-Com software. It can be used with standard distributors, coil-on-plug and coil-near-plug setups, crank triggers, and just about any possible engine combination using up to 16 injectors and making up to 4,000 hp.

13/20COMP Cams' adjustable cam gears for the 4.6-liter use six bolts to positively hold the gear in place. Fortunately, all it takes is removal of the valve covers to adjust cam timing, and not removing the whole front of the engine.

MME modified their Holley 4150 by adding a Throttle Position Sensor to it so they could use it as their throttle body and eliminate any question of whether the design of the throttle body/carb would alter power output. After inputting the basic dimensions of the engine into the C-Com software, they fired it up and were pleased with how easy it was to get it dialed-in and start making pulls. Typically with EFI, the easiest way to start is with the base map generated by the ECU, which is what they did. This was followed by short pulls to increasing rpm levels while making small changes and verifying that everything was copacetic. By easing into dyno pulls, it was no problem to dial in part-throttle and tip-in performance, which is where most tuners start to run into trouble. With years of EFI tuning and the easy XFI software, it was no problem for Mark. Once the fuel map was roughed in, they spent a good deal of time with full-range rpm pulls getting everything fine-tuned.

"All the testing that I did with carbureted and fuel injected was with the same carburetor and the same manifold. The good part about doing the testing the way I did was that I used the carburetor as the actual throttle body. That takes anything out of the equation of whether one was a restriction or the other. And just to see if it was a restriction, I did test with a 100mm throttle body." It was so big that under wide-open throttle, it was the same as essentially running with an open intake. What did he find? "Nothing," Mark says. "It made identically the same power."

14/20Since the engine has a Y-block design, dropping the sides of the block all the way to the ends of the main caps, the oil pan is quite shallow. It does benefit from built-in scrapers and some pans have an extra "pouch" welded to the side of the sump for extra capacity.

Asking Mark what the overall difference was between the carburetor and fuel injection, he says: "You know what, I didn't find anything between the two of them. You can overlay the carbureted version with the injected version, and it is so close to identical you could hardly tell the difference from one to the other. Even the air/fuel ratio was the same." Looking back at previous engines and data, Mark suggested that differences in the two setups and more specifically comparing individual cylinders' air/fuel ratios compared to power output, it was not so much whether or not the engines used a carburetor or EFI, but rather the design of the intake and exhaust systems and the way that they correspond to cam timing events. The pulses of air through the engine and out the exhaust have more of an effect on the engine's output than the method of fuel delivery.

"My preliminary theory on the carburetor was that it was going to be so much worse due to the fact that the manifold has right-angle turns in it. But you actually get a better, denser charge with the carburetor than you do with the injector. I think the injector has got a little better potential to put the actual fuel itself into the chamber, simply because it's aimed directly at the back of the intake valve. I think there's definitely positive power to be made with a carburetor over injection on certain manifolds because you get a cooler, denser charge, and the fuel is better atomized. However, on this particular manifold, I think that part of it is negated because of the design of the manifold. Having a plus and a minus gave you a zero."

15/20Shelf-stock Probe rods and pistons make the combination practically fall together to save big dollars. The relocated and oversized intake valve did, however, require fly-cutting the pistons.

When asked as a side question whether he had tried to run both a carburetor and fuel injection at the same time to take advantage of both systems' positive inputs, Mark's simple yet slightly evasive answer was "yes." Was it beneficial? "Yes." Take that as food for thought and discuss amongst yourselves.

White or wheat? Soup or salad? Carburetor or fuel injection? The answer might be as simple or complex as you want to make it, but in the end, it may be a matter of personal taste and the confines of your components.

16/20With the CNC-finished chambers, it is easy to see the difference in valve angle between the intake and exhaust valves. With a time deadline rapidly approaching, Mark barely had time to finish porting the heads before setting them directly on the engine.